Ochronotic Arthropathy and Alkaptonuria (Ochronosis): Case Report.

Alkaptonuria (AKU) is a rare genetic condition resulting from a deficiency in the homogentisic acid oxidase enzyme, which is produced by the liver and kidneys, that interferes with the metabolism of the amino acids phenylalanine and tyrosine. Although it may not cause symptoms, AKU can lead to ochronosis, the abnormal accumulation in body tissues of a pigment called alkapton. Over time, this pigment accumulation in the joints may result in secondary osteoarthritis known as ochronotic arthropathy, the most debilitating form of the disease. Since this is a rare condition, not widely discussed, we herein report a case to describe a diagnosis of ochronotic arthropathy of the knee only identified during surgery. Given the rarity of this condition, especially in Brazil, case descriptions will help understand the national epidemiology and disseminate more information about alkaptonuria and its clinical manifestations, particularly those of osteoarticular nature.